Dynamic subauroral ionospheric electric fields observed by the Falkland Islands radar during the course of a geomagnetic storm

first_imgWe present an analysis of ionospheric electric field data observed during a geomagneticstorm by the recently deployed HF radar located on the Falkland Islands. On 3 August2010 at ∼1800 UT evidence of the onset of a geomagnetic storm was observed in groundmagnetometer data in the form of a decrease in the Sym‐H index of ∼100 nT. Themain phase of the storm was observed to last ∼24 hours before a gradual recovery lasting∼3 days. On 4 August, during the peak magnetic disturbance of the storm, a high velocity(>1000 m s−1) channel of ionospheric plasma flow, which we interpret as a subauroralion drift (SAID), located between 53° and 58° magnetic south and lasting ∼6.5 hours, wasobserved by the Falkland Islands radar in the pre‐midnight sector. Coincident flow datafrom the DMSP satellites and the magnetically near‐conjugate northern hemisphereBlackstone HF radar reveal that the SAID was embedded within the broader subauroralpolarization streams (SAPS). DMSP particle data indicate that the SAID location closelyfollowed the equatorward edge of the auroral electron precipitation boundary, whileremaining generally poleward of the equatorward boundary of the ion precipitation. Thelatitude of the SAID varied throughout the interval on similar timescales to variations inthe interplanetary magnetic field and auroral activity, while variations in its velocity weremore closely related to ring current dynamics. These results are consistent with SAIDelectric fields being generated by localized charge separation in the partial ring current, butsuggest that their location is more strongly governed by solar wind driving and associatedlarge‐scale magnetospheric dynamics.last_img read more